1. Technical Field
The present invention relates in general to an improved disk drive, and in particular to an improved pivot assembly for a disk drive. Still more particularly, the present invention relates to an improved actuator bearing design in a pivot assembly for a disk drive for improving the performance of the disk drive.
2. Description of the Related Art
Generally, a digital data storage system consists of one or more storage devices that store data on storage media such as magnetic or optical data storage disks. In magnetic disk storage systems, a storage device is called a hard disk drive (HDD), which includes one or more hard disks and an HDD controller to manage local operations concerning the disks. Hard disks are rigid platters, typically made of aluminum alloy or a mixture of glass and ceramic, covered with a magnetic coating. Typically, several platters are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute.
Within most drives, one read/write head is associated with each side of each platter and flies just above or below the platter""s surface. Each read/write head is connected to a semi-rigid arm apparatus which supports the entire head flying unit. More than one of such arms may be utilized together to form a single armature unit. Each read/write head scans the hard disk platter surface during a xe2x80x9creadxe2x80x9d or xe2x80x9cwritexe2x80x9d operation. The head/arm assembly is moved utilizing an actuator having an actuator body mounted on a pivot assembly. The actuator is often a voice coil motor (VCM) having a stator that is mounted to a base plate or casting. The base casting is also the foundation for a rotatable spindle that supports the disks. The base casting is mounted to a frame via a compliant suspension. When current is fed to the motor, the VCM develops force or torque which is substantially proportional to the applied current. As the read/write head nears the desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
Modern HDD throughput and storage capacity have been substantially increased by improvement in actuator design which has resulted in increased precision and speed in head placement. The more precisely the actuator can place the read/write head, the greater the track density of the drive. However, rotary actuators have structural resonance modes that can affect disk drive performance. Some structural modes apply a reaction force against the pivot bearing, thereby tilting or rocking the actuator body on the pivot. Angular displacements of less than a milliradian of actuator tilt will cause the heads of the drive to go off-track.
For example, as shown in FIG. 1, a stacked actuator pivot has a pair of actuator bodies 43, 45 that are pivotally mounted to a shaft 47. When both actuator bodies 43, 45 are seeking on the same shaft 47, their combined forces can cause shaft 47 to deflect in an arc. This deflection results in out-of-phase and in-phase tilting of the fundamental vibration mode, which is also known as the xe2x80x9cbutterflyxe2x80x9d mode. The center of the deflection force during seeking on the stacked actuator pivot is not located at the center of shaft 47. This causes the heads 49 on the arms 51 nearest the axial center of the pivot to deflect the most, as depicted on the left side of FIG. 1 by blocks 3 and 4. In contrast, the heads 53 on the axially outermost arms 55 deflect the least, as depicted by blocks 0 and 7. Actuator pivot tilting is problematic for head switching track misregistration (TMR), which degrades the performance of the disk drive. Thus, an improved apparatus and method for overcoming deflection of actuator pivots is needed.
One embodiment of a disk drive pivot assembly design has a shaft that supports two actuators. The pivot assembly design compensates for the tilting of the actuators due to shaft bending during seek operations. Two types of bearings of differing stiffness are used to achieve improved performance. The axially innermost bearings are stiffer than the axially outermost bearings, which are relatively compliant. By having two different bearing stiffnesses, the boundary conditions of the pivot assembly are adjustable and can compensate for shaft bending, which is greatest near the center of the pivot assembly. Track misregistration due to actuator tilt is decreased by compensating the shaft deflection through appropriate stiffening of the pivot.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.